1. Field of the Invention
This invention relates to abrasive grinding wheels, and more particularly to an improved wheel hub for mounting a grinding wheel to a grinding apparatus.
2. Background Information
Grinding machines that utilize abrasive grinding wheels mounted therein may be employed to perform many distinct grinding operations. The varied operations have led to the development of a wide variety of grinding wheel shapes and sizes. One type of grinding wheel in particular is the depressed center wheel, characterized by the central portion of the wheel being offset in the axial direction from the wheel periphery. The wheel thus has a concavo-convex stub portion in which a grinding face has a depressed or concave central portion and an opposite backing face has a raised or convex central portion. This design allows a user to perform face grinding operations using the grinding face having the depressed central portion. Often, such operations are performed on metal, masonry or concrete surfaces and the like, using portable grinding machines. Depressed center wheels are classified by the American National Standards Institute (ANSI) as Type 27 and 28 grinding wheels.
The means by which a grinding wheel is secured to the grinding machine spindle is particularly important with depressed center wheels. In general, the mounting means must be capable of holding the wheel perpendicular to the spindle during grinding operations, and must provide support to the wheel to distribute stresses away from the central mounting aperture, where stresses tend to concentrate. The mounting means also must be firmly secured to the abrasive wheel, to prevent any slippage therebetween. In addition, the mounting means for Types 27 and 28 wheels have generally been provided with extra support to the wheel periphery, as well as to the central portion of the backing (non-grinding) face of the wheel to resist the additional stresses imposed by face grinding operations.
To satisfy these requirements, it is common to provide Type 27 and 28 wheels with a hub having a flange that extends over the central raised portion, the concavo-convex stub portion, and onto and in contact with the peripheral portion of the wheel, to resist side pressure or otherwise uneven force applied to the grinding face of the wheel. The opposite face of the wheel is provided with a flange contained completely within the depressed area thereof.
Although such hub construction may produce satisfactory results in many instances, it is not without drawbacks. In particular, extension of the flange beyond the raised stub portion of the backing face tends to limit the useful life of the wheel. In this regard, the wheel must be replaced before it is ground down to the diameter of the backing flange to avoid potentially damaging contact between the backing flange and the workpiece. Accordingly, grinding wheels that utilize this hub construction tend to be discarded with a substantial portion of valuable and otherwise usable abrasive remaining thereon. Such relative under-utilization of the wheel tends to add undesirable expense to grinding operations in terms of both wheel cost and labor costs associated with the frequency of wheel removal and installation.
A need thus exists for an improved grinding wheel hub that overcomes the drawbacks of the prior art.